Implement [Inline] interfaces

Inline interfaces just appear as a Rust type and in the TypeId hierarchy.
They are completely invisible on the JS side.

components/script/dom/globalscope.rs

@@ -0,0 +1,18 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use dom::eventtarget::EventTarget;
+
+#[dom_struct]
+pub struct GlobalScope {
+    eventtarget: EventTarget,
+}
+
+impl GlobalScope {
+    pub fn new_inherited() -> GlobalScope {
+        GlobalScope {
+            eventtarget: EventTarget::new_inherited(),
+        }
+    }
+}